1. Field of the Invention
The present invention relates to compositions comprising a concentrate of polyalkylene terephthalate with a phosphorus-containing additive, which compositions are distinguished by high melt stability, and to a process for the preparation of impact-modified polyalkylene terephthalate/polycarbonate compositions, wherein a concentrate of polyalkylene terephthalate with a phosphorus-containing additive is used.
2. Description of Related Art
The stabilisation of polyalkylene terephthalates with esters of phosphoric acid is known. The esters of phosphoric acid can react with catalysts from the transesterification or from the polycondensation that are still present in the polyalkylene terephthalate and thus lessen a parameter influencing the polycarbonate/polyester transesterification reaction. Although the precise mechanism is not yet known, the effectiveness of stabilisation with the aid of esters of phosphoric acid has been described many times, such as, for example, in “The role of phosphates in stabilization of non-polyolefin polymners”, Ashton, Henry C.; Enlow, William; Nelen, Tim, G E Specialty Chemicals Inc., Morgantown, W. Va., USA, Annual Technical Conference-Society of Plastics Engineers (2000), 58th (Vol. 3), 2818-2825 or in “Inhibition of transreactions in condensation polymers”, James, N. R.; Mahajan, S. S.; Sivaram, S., Division of Polymer Chemistry, National Chemical Laboratory, Pune, India., Editor(s): Fakirov, Stoyko., Transreactions in Condensation Polymers (1999), 219-265; Publisher: Wiley-VCH Verlag GmbH, Weinheim, Germany.
U.S. Pat. No. 4,066,617 discloses polyalkylene terephthalates containing esters of phosphoric acid with oxetan groups. WO 2004/007607 A discloses polymers phosphoric acid esters with oxetan groups. The use of carboxyalkylphosphoniic acid as auxiliary agent for the preparation of polyesters is disclosed, for example, in U.S. Pat. No. 5,744,572.
US 2002/0137823 discloses compositions comprising polyesters and esters of phosphoric acid, which compositions are distinguished by improved hydrolytic stability.
Phosphoric acid in a low concentration and used in the form of an aqueous solution is used to stabilise polycarbonate/polyester compositions (see, for example, Examples 7 to 10 of U.S. Pat. No. 6,635,698).
EP 0 294 862 A discloses the stabilisation of polycarbonate/polyester compositions with the aid of a combination of a phosphorus-containing stabiliser and elemental sulfur. EP 0 683 200 A describes the advantages of stabilising polycarbonate with the aid of phosphorus-containing acid and esters of a phosphorus-containing acid.
In the prior art, the stabilisers are used in a concentration of up to 1 to 2 wt. % and the stabilisers are in each case, generally added directly to the mixture.